Refrigeration



Dec. 3, 1940. H POWNALL 2,223,900

REFRIGERATION Filed May 22, 1939 3 Sheets-Sheet l TH ERMAL BULB 1 H EATEXCHANGER.

CONDEN5EQ. (2Q 85 RECEIVER FLOODED EVAPORATOR/ EXPANSION SOLENOID VALV EVALVE TH EXPANSION VALVE.

CONDENSER. 1 1; {3 RECEJVEJZJ BY-PASS Ll ul D 2 2(1) SOLENOID EXPAN 5|ON VALVE.

SPRAY TYPE WATER COOLER,-

EVA 90 RATO R,

Ja s

Z'mventor (Zttomegs 1 H. B. POWNALL 2,223,900

REFRIGERATION Filed lay 22. 1939 3 Sheets-Sheet 2 20 If IIIIII r I?23*9/K 150.,

ll fi I 5 F I a 58% r [I I D 3, 1940- H. B. POWNALL 2,223,900

REFRIGERATION Filed May 22, 1939 3 Sheets-Sheet 3 Zmventor Patented Dec.3, 1940 UNITED STATES REFRIGERATION Henry B. Pownall, York, Pa.,assignor to York Ice Machinery Corporation, York, Pa., a corporation ofDelaware Application May 22, 1939, Serial No. 275,099

Claims.

This invention relates to refrigeration, and particularly to means forreturning to the compressor lubricating oil which leaves the compressorwith the compressed refrigerant and, in

6 the absence of special means to remove it, tends to accumulate in theevaporator.

Many schemes have been proposed to accomplish oil return, and thosewhich have been successful have, so far as applicant is aware, in-

10 volved withdrawal of a mixture of refrigerant and oil from theevaporator, the separation of the refrigerant and oil by fractionaldistillation, followed by the return of the refrigerant to the circuitand the return of the oil to the compressor, usually to the crank casethereof.

These schemes require the use of considerable additional apparatus withattendant wasteful evaporation of liquid refrigerant, and many of themare characterized by inability to operate satisfactorily over the entireload range of the refrigeration circuit. Diiiiculty is also encounteredwith such systems where the compressor runs at various volumetric rates,as is the case in installations in which the compressor is driven atvariable speed. or if driven at constant speed is subject to stepunloading or progressive unloading.

According to the present invention, the oil is caused to leave theevaporator with the refrigerant and flow toward the compressor throughthe suction line, the refrigerant which is then in the vapor phase iscompressed by the compressor and the oil is returned to the crank caseof the compressor. Thus the evaporation of the refrigerant producesuseful refrigeration. The invention affords simple means for effectingthe desired separation at the compressor inlet. Systems equippedaccording to the invention will operate satisfactorily even when thecompressor runs at different speeds or at Variable volumetric rates oris shut down from time to time. The invention can be applied to spraytype evaporators, to flooded evaporators, and in fact to nearly anytype.

The characteristics of operation vary somewhat with the load, but properdesign permits a balance to be struck such that the oil return issubstantially uniform. Consequently depletion of oil in the crank casedoes not occur even if the plant operates at some particular unfavorableload for a long period. This last condition is one which impairs theoperation of many of the prior art schemes.

Generally stated, the compressor delivers to the usual condenser and themain path of refrigerant from the condenser to the evaporator is by wayof a thermal expansion valve. The thermostatic bulb of such valve isapplied to the suction line and thus controls the rate of supply ofrefrigerant to the evaporator in such a way 5 that all refrigerantflowing to the compressor is slightly superheated and is, therefore,necessarily in the vapor phase.

Interposed between the evaporator proper and that portion of the suctionline to which the 10 thermal bulb just mentioned is applied, is asuperheating heat-exchanger comprising a shell through which therefrigerant leaving the evaporator fiows. In the shell is a finned heatexchange coil, through which a small quantity of i5 liquid refrigerant,less than the minimum amount needed by the evaporator, flows.

Such refrigerant is tapped oil? from the liquid line between thecondenser and the thermal expansion valve, flows thence through the coilof 0 the heat exchanger, thence through a normally open stop valve (suchas a magnet valve) which closes as an incident to stoppage of thecompressor and thence through an expansion valve, which, for simplicity,is of the manually adjusted 25 type, to the evaporator. This manuallyadjusted expansion valve is so set that the heat exchanger willsuperheat refrigerant leaving the evaporator under all load conditionsencountered. Consequently the superheater affects the operation 30 ofthe thermal expansion valve, with the result that the expansion valvesupplies to the evaporator the variable demand for refrigerant in excessof that supplied by the manually operable expansion valve. 35

It is important at this point to explain the effects of variable heatload on the evaporator.

If the quantity of oil in the compressor crank case is to beapproximately constant, the quan-- tity of oil which is permitted toremain in the 40 evaporator must be approximately constant, it beingobvious that the quantity of oil in other parts of the system is notsubject to material variation.

The thermal expansion valve is set to feed 45 more refrigerant to theevaporator as the superheat in the gas passing through the suction lineincreases. When the evaporator is subjected to a sudden change from arelatively heavy to a lighter heat load, the liquid level in the evapo-50 rator lowers. As a result of the lowered liquid level the gaseousrefrigerant leaving the heat exchanger tends to increase in superheat.The thermal valve responds to increase the flow of refrigerant to theevaporator, thus raising the 55 liquid level therein. If the liquidlevel rises until slugs of liquid enter the heat exchanger, thesuperheat decreases and the expansion valve reduces the rate of feed ofrefrigerant. Ultimately equilibrium is reached between the rate ofliquid feed and the heat load.

Conversely, when the evaporator is subject to a change from a relativelylight to a heavier load, the heat supplied to the liquid causes activeevaporation and the entrainment of liquid refrigerant tends to reducethe superheat of the gaseous refrigerant leaving the heat exchanger. Thethermal valve responds and reduces the rate of liquid feed to theevaporator until a balance is reached between heat load and liquid feed.In this phase the liquid level lowers until the superheat causes thethermal valve to open sufficiently to establish equilibrium.

An important element of the invention is the heat exchanger which notonly superheats the gaseous refrigerant passing the thermal bulb so thatthe thermal valve functions more effectively regardless of changes ofheat load on the evaporator, but also serves to heat the mixture of gasand entrained oil under conditions which prevent reflux of the oil tothe evaporator.

Whether this refrigerant-oil mixture enters the exchanger in the form offoam, or assumes the foam form in the exchanger (and either or bothactions may occur, according to load conditions) the efiect is toseparate the gaseous refrigerant from the mixture at a point where thegaseous refrigerant is flowing rapidly so that the oil is caused to flowwith the gaseous refrigerant through the suction line.

The effect is to assure oil return under all conditions of operation andstimulate the return as the oil concentration in the evaporatorincreases, so that the absolute quantity of oil in the evaporatorremains nearly constant. This action can be explained as follows:

Under conditions of light load the evaporator is nearly filled, so thatliquid'refrigerant with a small percentage of oil slops into the heatexchanger where the liquid refrigerant is evaporated and slightlysuperheated. When the refrigerative load is heavy, and less liquidrefrigerant is in the evaporator, the concentration of oil in therefrigerant exceeds the point at which active foaming in the evaporatorwill occur. Consequently, the evaporator fills with oil filmed bubblesand the vaporous refrigerant flowing from the evaporator into thesuperheater takes the form of a stream of oily bubbles. The refrigerantis superheated in the heat exchanger and as before entrains the oil andcarries it to the compressor.

Thus the oil return has two phases of operation in each of which theheat exchanger performs the useful function of supplying the finalsuperheat. When the concentration is below that necessary to producefoaming, the tendency of liquid refrigerant to enter the heat exchangeris at a maximum and ensures oil return. When the concentration reachesthe foaming stage, the foam carries the oil through the relativelylonger vertical interval above the liquid level in the evaporator to theheat exchanger.

The amount of liquid refrigerant flowing through the coils in the heatexchanger is fixed by the manually adjustable expansion valve and isless than the minimum demand for refrigerant imposed by the evaporatorwhen the system is operating. The thermal expansion valve stabilizes theentire circuit and controls the liquid level in the evaporator inaccordance with the heat load. If the compressor is stopped, thesolenoid stop valve closes and terminates the flow of liquid refrigerantthrough the heat exchanger until the compressor is again put inoperation. The action is such that the total quantity of oil in theevaporator tends to remain uniform, and this fact is an importantconcept underlying the invention.

Preferred embodiments of the invention will now be described withreference to the accompanying drawings, in which Figure l is adiagrammatic view of a refrigerating circuit using a flooded evaporatorand having the invention applied.

Figure 2 is a similar view showing a refrigerating circuit of a slightlydifferent type with the invention applied. In this view the evaporatoris shown as a spray type water cooler and the circuit is supposed to beone of relatively large capacity, so that a thermostatic valve oflimited capacity is used to control a liquid regulating valve of acapacity adequate for the system, the regulating valve performing theactual control of the main flow of liquid from the condenser to theevaporator.

Figure 3 is a fragmentary view showing an alternative location of theheat exchanger which might be used in the structure of either Figure lor Figure 2.

Figure 4 is a vertical axial section through the heat exchangerindicating a construction which has been successfully used in practice.

Figure 5 is a section on the line 5-5 of Figure 4.

Figure 6 is a view partly in section and partly in elevation, showingthe liquid regulator valve.

Figure 7 is a view partly in elevation and partly in section showing atwo-cylinder compressor with trunk pistons and side suction inlets, theinlet valves being in the piston heads. This is a type of compressorwith which the invention has been successfully used.

Figure 8 is a diagrammatic view partly in section and partly inelevation of an unloader mechanism which is incorporated in thecompressor of Figure 7 While the invention will be here described asused with a compressor having a variable volumetric rate, this showingis made chiefly to include an affirmative disclosure of such anarrangement. The invention can be applied with compressors which aremerely started and stopped and which, when they operate, operate at aconstant volumetric rate.

The particular unloading mechanism here illustrated is described andclaimed in the patent to Aldinger, No. 2,036,847, April 4, 1936, and sofar as the present invention is concerned, is simply an example of onemeans for Varying the volumetric rate of the compressor. Variation ofthe volumetric rate is the essential point and any known means forcausing it may be used. One reason for using compressors of varyingvolumetric capacity is to stabilize evaporator temperature despite loadvariations. The invention is applicable to such systems but is not inany sense limited thereto.

Referring first to Figures 1, 4, 5, 7 and 8, the refrigerating circuitcomprises a compressor 1 l driven by a motor such as the electric motorl2 and connected by way of the high pressure discharge line l3 with thecombined condenser and receiver 14 of any suitable type.

From the condenser It the liquid line [5 leads to a thermal expansionvalve l8 which delivers refrigerant through connection H to a floodedevaporator Hi. The evaporator I8 is connected by way of connection I9with the shell 20 of the heat exchanger. The top of the shell isconnected to the suction line 2| which leads to the suction of thecompressor hereinafter described in greater detail.

From the liquid line |5 a branch 22 leads to the upper end of the shell20, where it communicates with a heat exchange coil generally indicatedby the numeral 23 on Figure l, and this coil connects at the lower endof the shell 20 with a line 24 which leads through the solenoid stopvalve 25 and manually adjustable expansion valve 25 to the inletconnection H in the evaporator. Valve 25 is urged closed by a spring(not shown) and opens when winding 21 is energized. Such solenoid valvesare well known.

The winding 21 of the solenoid valve and the motor |2 are bothcontrolled by a switch diagrammatically illustrated at 28 as a knifeswitch, so that when the switch is closed and the motor l2 runs, thesolenoid valve 25 is wide open, and when the motor I2 is stopped, thesolenoid valve 25 is closed tightly by the spring above-mentioned.

The expansion valve is of a type common in the art, in which therefrigerant pressure on the discharge side of the valve acts on 9.diaphragm or other movable abutment connected with the valve in such away that rising pressure on the discharge side of the expansion valvetends to close the expansion valve.

Connected with the expansion valve I5 is a thermal bulb 29 which isapplied to the suction line 2| near the point at which this line isconnected with the upper end of the shell 20. The bulb 29 is subject tothe temperature of the suction line and contains an expansible fluid ofsuitable character which develops pressure on rising temperature, thepressure being transmitted through the tube 3| to a diaphragm orabutment within the valve H; in such a way that rising temperature atthe bulb 29 tends to open the expansion valve.

Such valves commonly include an adjustable biasing spring. Any type ofthermostatic expansion valve may be used, provided it is of a typesuited to control the superheat in the suction line 2| near itsconnection with the shell 20. Inasmuch as such expansion valves arestandard articles of commerce, no attempt to illustrate details has beenmade.

The expansion valve 26 is just a manually adjustable throttling valve ofconventional form.

The compressor II is preferably of the type illustrated in Figure 7. Thegrooved belt wheel 32 drives a crank shaft (not shown) and this shaftdrives through connecting rods 33 a pair of trunk pistons, one of whichappears at 34. These trunk pistons have packing rings on the upper headat 35 and the inlet valve is mounted in the piston and is of the suctionoperated type. The lower end of the piston is simply a guiding memberand carries an oil scraper ring indicated at 36. This ring is not apacking ring, but is designed to act on oil on the cylinder walls andfeed it downward into the crank case 31. Such rings are in extensive usein compressors and in gasoline engines.

The suction line 2| enters through the cylinder wall by way of the port38 and thus communicates with the middle portion of the piston betweenthe packing rings 35 and the oil ring 35.

It follows that the crank case is substantially at suction pressure,although the communication between the crank case and the suctionconnection is somewhat restricted.

Such compressors may be run at variable speed, but because most drivingmotors are of the alternating current type, the usual practice is to runthe compressor at constant speed and provide an unloader to vary itsvolumetric rate. The compressor shown in the drawings is so equipped.

Referring to Figure 8, the combined unloader piston and valve 4| isshown in its loading posi-.

tion in which it closes the by-pass or unloading port 42 in the cylinderwall. These ports are located at part stroke so that they will beovertraveled by the piston, say at half stroke. If the ports are openthe piston does not start compression until it has overtraveled theports.

The stem 43 operated by hand wheel 44 is merely a manually adjustablemeans, operable to lock the piston 4| in its loading position. Normallyit is retracted, as shown.

The unloading piston and valve is operated by refrigerant under pressurepreferably derived from the discharge connection of the compressor, asexplained in the Aldinger patent above mentioned. Two pressureconnections are shown at 45 and 46 and they are controlled by a pistonvalve 41 which is biased in one direction by a spring 48 and may beshifted against such bias by a piston 49. The pressure acting on thispiston is controlled by a needle valve 5| which is closed when thewinding in the case 52 is deenergized and open when that winding isenergized. The energization of the winding 52 may be controlled by anymeans, but since such control is not material to the present invention,none is illustrated.

Known controls, for example, are thermostatic switches responding tovarious temperatures, and pressure switches responding to suctionpressure in the system. So far as the present invention is concerned,the material point is that the oil return system will operatesatisfactorily with compressors operating at varying volumetric rates.It will also operate with compressors which operate at constantvolumetric rates and are merely started and stopped.

The construction of the superheating heat exchanger is shown in detailin Figures 4 and 5. The shell 20 is provided with a removable head asshown. The coil structure indicated generally by the numeral 23 inFigure 1 takes the form of three adjacent coils connected in parallelbetween an upper inlet header 55 to which the branch 22 is connected anda lower discharge header 56 from which the line 24 leads. These coilsare spirally finned, the fins being indicated at 51 in Figures 4 and 5,but omitted elsewhere because they would obscure the view.

To all intents and purposes, the shell 20 is filled with a mass offinned tubing. The particular form of the finned coils is not deemed tobe vitally important, provided it is adapted to exert what may bedescribed as an eliminator effect. By this is meant that the fins andthe tubes arrest liquid which may enter the shell 20 through theconnection I9 and hold the liquid in contact with the heat exchangesurface until the refrigerant is completely evaporated. The oil willadhere to the extended finned surface in such a way that it may readilybe entrained by the vaporous refrigerant flowing rapidly from the shell20 to the suction line 2|.

It will be observed that perforated plate diaphragms 58 and 59 extendacross the shell 20 above and below the coils and that the lowerdiaphragm 58, together with the lower discharge header 58, resists thetoo free surging of liquid entering at I9 upward through the shell 20.

The effect is to offer a large heat exchange and liquid arrestingsurface to enable heat to flow from the warm liquid to the refrigerantleaving the evaporator so that the heat performs a final refrigerantsuperheating function under conditions which favor the entrainment ofoil and its delivery to the suction line 2I.

As has been described, when .the heat load on the evaporator is low, thethermal valve causes the evaporator to fill nearly full. The refrigerantevaporating in the evaporator then causes liquid to slop through theconnection I9 into the shell 20 where the liquid refrigerant componentwill be evaporated by heat derived from the warm liquid flowing throughthe coil structure 23. Thus oil concentration occurs in the heatexchanger, foam forms in the exchanger and the oily foam flows to thecompressor.

Under heavy load conditions, the liquid level in the evaporator islower, the oil concentration is higher, and active foaming occurs in theevaporator itself. This foaming carries oil into the shell 20 and thisoil is entrained with off-flowing refrigerant as before.

Under intermediate conditions there may be different degrees of foamingin the evaporator and different degrees of slopping of liquidrefrigerant into the shell 20.

It is difllcult to prescribe the operation precisely because underoperating conditions it is impracticable to see what takes place, butextensive tests have shown that the operation of the system is stable,so that the absolute quantity of oil in the evaporator tends to remainnearly constant, regardless of the heat load or volumetric rate of thecompressor, with the result that the quantity of oil in the crank case31 also tends to remain nearly constant. The fact of operation isdemonstrated. The best known theory of what occurs has been stated.

The arrangement shown in Figure 2 is essentially similar to that shownin Figure 1. Those parts which are identical with similar parts inFigure 1 are given the same reference numeral with the letter a.

The differences will now be specified. The expansion valve IBa does notdirectly control the main flow of refrigerant. The liquid line I5a fromthe condenser Ma leads to a liquid regulator valve GI which is shown indetail in Figure 6. This has a balanced poppet valve unit 61 operated bya diaphragm 68 which is loaded by a spring 69 in a closing direction andwhich is subject in a valve opening direction to the pressure in thehigh pressure liquid line I5a. The space above the diaphragm 68 isclosed by a cap H which serves not only as a seat for the spring 69 butalso as a pressure chamber for loading the diaphragm 68 in a closingdirection.

A choke I4 is interposed in a branch line 12 and supplies refrigerant tothe line l3 which is connected to the inlet of the thermal expansionvalve Mia and with the space in cap lI above diaphragm 68. Expansionvalve I6a delivers to the line Ila.

Thus the valve 16a responds to the temperature at the bulb 29a acting inopposition to the pressure in the line Ila and exercises a control onthe valve 61 which thus responds to the combined effect of temperatureand pressure. Hence the liquid regulator BI is simply a large capacityvalve whose opening and closing has the same flow controllingcharacteristics as does the expansion valve IBa. This is simply aconvenient way of getting large capacity regulation by the use of asmall thermal expansion valve. No novelty is here claimed for thatarrangement.

The evaporator I8a is indicated as a spray type water cooler, the liquidrefrigerant being fed by the connection Ila into a spray pipe I817. The

water to be cooled passes through tubes within the evaporator over whichthe refrigerant showers. These tubes are not illustrated as they wouldsimply complicate the drawings. The structure of the cooler is wellknown and is not a feature of the invention.

Figure 3, on which are applied the same reference numerals as those usedin Figure 1, involves no material change of construction but only achange of location. The purpose of the view is merely to indicate thatthe shell 20 need not be directly above the evaporator I8, although thatlocation is preferred.

Where head room does not permit, the exchanger may be located to oneside of the evaporator and even at a slightly lower level, as shown inFigure 3. The operative characteristics are essentially similar.Obviously the arrangement shown in Figure 3 could be used with thescheme of Figure 2 in case of necessity.

With reference to all embodiments of the invention, it may be noted thatthe system operates with a wet discharge from the evaporator, that is,the evaporator is so designed that it foams or primes or foams andprimes. The final evaporation and superheat of refrigerant are securedby heat exchange with a portion only of the liquid refrigerant flowingto the evaporator. It

- has not been found practicable to use in the heat exchanger all theliquid refrigerant flowing to the evaporator because where sucharrangements have been attempted, a persistent and objectionable cyclingtakes place.

The thermal expansion valve is used to ensure changes of level of liquidin the evaporator as an incident to changes of load. The device is socontrived that when the oil concentration is high and foaming occurs,the foam is caused to carry the oil into the heat exchanger drum. Whenthe oil concentration is low, and foaming is less or does not occur,priming and slopping over into the heat exchanger serve to carry oilinto the exchanger.

Close spacing of the coils and of the finned surface in the exchangerfunctions to arrest liquid refrigerant, ensure its evaporation, and toretain the oil in a dispersed condition favorable to entrainment by therapidly off-flowing vaporous refrigerant.

While the controlling factors in design cannot be stated with precision,it has been found that adjustment of the expansion valve 26 will permitthe operation to establish a stable condition under which there is aninherent tendency for the absolute quantity of oil in the evaporator toremain constant. Because it does remain constant, there is an inherenttendency for the quantity of oil in the compressor crank case to remainconstant.

The idea of returning the oil with the refrigerant to the inlet of atrunk piston, side inlet compressor is an important feature of theinvention. It offers a remarkably ood oil separation. While the theorymay be erroneous and is not material to the invention, it is believedthat the oil contacts the piston and adheres to it by capillaryattraction, so that the refrigerant flows freely through the inlet valveand the oil flows to the oil ring and is progressively returned to thecrank case by the oil scraping action thereof.

However this may be, the oil return mechanism involves very littleaccessory apparatus. The superheat imparted to the refrigerant in theshell 20 is derived from a portion of the liquid refrigerant flowing tothe evaporator, so that the efficiency of the circuit is not penalized.The system requires no periodic attention. It contains no flow traps andno by-pass connections from the evaporator to the compressor.Consequently, the efliciency of the refrigerating circuit is notimpaired and the circuit cannot be bypassed by the accidental stickingof any by-pass controlling valve. The separation of the oil and therefrigerant occurs at a time when the refrigerant is superheated andhence is in the vapor phase. From this it follows that liquidrefrigerant does not find its way to the crank case of the compressor.

While several embodiments of the invention have been described inconsiderable detail, these descriptions are intended to be illustrativeof the best known embodiments, and are not intended to be limiting. Thescope of the invention is defined in the claims.

What is claimed is:

1. The method of limiting the accumulation of oil in the evaporator of arefrigerator circuit of the compressor-condenser-evaporator circuit typecharged with a refrigerant in which the oil is soluble which comprisesthe refrigerant in the evaporator to foam, causing said foam to flowtoward the compressor; heating said foam as it flows toward thecompressor by heat exchange with warm liquid refrigerant flowing to theevaporator until substantially all refrigerant is in the vapor phase,varying the rate of total supply of refrigerant to the evaporatoraccording to evaporator pressure and the temperature of the foam aftersuch heat exchange to assure at least slight superheating of therefrigerant component of the foam and at least before passage throughsaid compressor, breaking down said foam and causing the oil andvaporous refrigerant to fiow in divergent paths.

2. The method of operating a refrigerating system of thecompressor-condenser-evaporator circuit type in which a volatilerefrigerant in which the compressor lubricant is soluble is used, whichmethod comprises balancing the tendency of oil to flow with refrigerantto the evaporator and accumulate in the evaporator by fractionaldistillation, by entraining lubricant with refrigerant flowing from theevaporator to the compressor, such entrainment being produced by sooperating the evaporator that the refrigerant foams and primes, causingfoam to flow toward the compressor, vaporizing liquid refrigerant insuch foam by heat exchange with a portion only of the liquid refrigerantflowing from the condenser to the evaporator, varying the rate of supplyof refrigerant to the evaporator according to evaporator pressure andthe temperature of the foam after such heat exchange to assure at leastslight superheating of the refrigerant component of the foam, andbreaking down such foam as it enters the compressor whereby thelubricant resumes its lubricating function and the vaporous refrigerantapproximately freed of lubricant is compressed.

3. The method 'of operating a refrigerating system of thecompressor-condenser-evaporator circuit type, in which the circulatedrefrigerant is of a type in which the lubricant used in the compressoris soluble, which method comprises limiting the rate of admission ofrefrigerant to the evaporator sufficiently to assure moderatesuperheating of vaporous refrigerant flowing to the compressor, withoutinhibiting priming and foaming in the evaporator; subdividing the liquidrefrigerant flowing from the condenser to the evaporator into twostreams which are distinct at least to the extent that they aresubstantially out of heat exchange relation with each other; supplyingheat to the foam leaving the evaporator by heat exchange with one ofsaid streams; and feeding the foam to the compressor whereby the foam iscaused to break down, the lubricant serving to lubricate the compressorand the vaporous refrigerant being compressed and discharged to thecondenser at least partially freed of lubricant.

4. A refrigerating circuit containing a volatile refrigerant andcomprising in combination, a compressor provided with lubricating meansusing a liquid lubricant soluble in said refrigerant; a condenser intowhich the compressor discharges; expansion valve means of the superheatcontrol type fed by the condenser and including a thermal element; anevaporator fed by said expansion valve means; a heat exchanger includinga shell connected to the evaporator above the maximum liquid leveltherein and containing a heat exchange element offering a flow path fora heating medium; a suction line leading from said shell to the suctionintake of said compressor, said thermal element being subject to suctiontemperature in said line; means for separating lubricant from gaseousrefrigerant as they approach the compressor; and a by-pass leadingfrom'said condenser to and through said heat exchange flow path to saidevaporator, said by-pass including means to control the rate of fiowtherethrough,

5. A refrigerating circuit containing a volatile refrigerant andcomprising in combination, a compressor provided with lubricating meansusing a liquid lubricant soluble in said refrigerant; a condenser intowhich the compressor discharges; expansion valve means of the superheatcontrol type fed by the condenser and including a thermal element; anevaporator fed by said expansion valve means; a heat exchanger includinga shell connected to the evaporator above the maximum liquid leveltherein and containing a heat exchange element offering a flow path fora heating medium; a suction line leading from said shell to the suctionintake of said compressor, said thermal element being subject to suctiontemperature in said line; means forming part of said compressor forseparating lubricant from refrigerant and comprising a cylinder scrapingring carried by the piston and arranged to divert lubricant and meansfor causing the entering mixture to impinge upon the piston; and aby-pass leading from said condenser to and through said exchange flowpath to said evaporator, said by-pass including means to control therate of flow therethrough.

6. The combination defined in claim 4 in which the flow through theshell from the-evaporator and the flow of liquid refrigerant through theflow path of the heat exchange element toward the evaporator are ingenerally opposite directions.

7. The combination defined in claim 4 in which the heat exchange elementtakes the form of a plurality of closely spaced finned tubes, the finsbeing generally parallel with the direction of flow through the shelland the coils extending across substantially the entire transverseextent of the shell.

8. The combination defined in claim 4, in which the means controllingthe rate of flow through the by-pass is a manually adjustable expansionvalve located between the heat exchange flow path and the evaporator.

9. The combination with the structure defined in claim 4 of a stop valveinterposed in said bypass; and valve controlling means arranged to opensaid stop valve when the compressor operates and close it at othertimes.

10. The combination with the structure defined in claim 4 of means forvarying the volumetric rate of the compressor.

CERTIFICATE OF CORRECTION.

Patent No. 2,225,900. December 19m.

HENRY B. POWNALL.

It is hereby certified that error appears in the printed specificationof the abovenumbered patent requiring correction as follows; Page 5,first column, line 55, claim 1, after the word "comprises insert"causing";

and thatthe said Letters Patent shouldbe readwith this correctiontherein that the same may conform to the record of the case in thePatent Office.

Signed and sealed this llpth day of January, A. D. 19M.

Henry Van Arsdale,

( Acting Commissioner of Patents.

